Flight, April 1934

THE DE HAVILLAND "DRAGON SIX"This week we are able to publish the first details to be released of an aeroplane developed to cater for the speeding up of air lines similar to those in this country. It is the inevitable result of steady development

SWITZERLAND is to receive the first "Dragon Six," as the model which is herein described has been bought by Herr R. Herzig, of the Ostschweiz Aero Ges. for operation on the line St. Gaul, Zurich and Berne, which will connect with the lines to Marseilles and Barcelona. Another of these new machines will also soon be on its way to South Africa The "Dragon Six," or D.H.89, to give it its works designation, is obviously the outcome of improving a standard "Dragon" in the light of knowledge gained with the four-engined D.H.86, which was described in FLIGHT of February 22, 1934. It resembles the latter machine perhaps even more than the standard "Dragon," because those improvements very largely consist of alterations to external features, of the kind which immediately catch the eye. For example, the wings are very like those of the D.H.86, that is, heavily tapered, with wire bracing in the front bay only. Similarly, each engine is mounted over one unit of the landing gear in a most distinctive manner. As will be seen from the table, by these improvements and by the use of two "Gipsy Six" engines, the cruising speed has been raised to 140 m.p.h. (225 km/h), and the machine has quite a considerable ceiling on one engine with full load. From a consideration of these main details it is immediately obvious that the "Dragon Six" is a machine which is particularly suitable for the development of air services in all parts of the world. The wing construction does not differ very much from that used in the D.H.86. The biplane structure is braced by one pair of streamline-section steel tube struts and one built-up steel strut of similar section. This strut is, incidentally, spot welded, a manufacturing process which de Havillands have not so far used very extensively. The top planes have spindled spruce spars throughout their entire length and each is in one piece as far as the root fittings either side of the top of the fuselage. The bottom wings have spars of the same construction as far as the pair of inter-plane struts. Inside those, the surface is in the form of a bottom centre section which carries the engines and landing gear, and each side is, of course, identical. In this centre section the front spar is a steel tube and continues from one side to the other under the floor of the fuselage. The leading edge of the wings is smoothly finished off with fabric covered plywood, and the ailerons, of which there are four, are completely covered with the same material. They are not balanced aerodynamically and are tapered to conform with the plan form of the wing. The ailerons in the top wing are operated by a push rod which is worked by a lever underneath the bottom plane, and led through the single strut between the wing tips, thereby doing away with external connecting gear to a great extent, and, of course, reducing drag considerably. All the inter-plane strut roots are carefully faired to the wing surface with light alloy "cuffs." The wing roots are similarly filleted and faired into the fuselage with sheet light alloy fairing. The engine and landing gear on each side form separate units. From each side of the wheel axle a tube runs straight up to the front spar, and carries in it a shock-absorbing strut designed and manufactured by Aircraft Components, Ltd., of Cheltenham, or, as it is perhaps better known, a Dowty leg. These tubes are braced to the rear spar by other steel tubes. In the front of this structure the engine mounting is carried, and this follows normal de Havilland design, being a welded up mounting of square section steel tubes. From the spars above the centre section, sloping struts of streamline section steel tube are carried up to the top of the fuselage. Behind the engine in each case is a welded aluminium fuel tank, the standard capacity being 40 gallons (182 litres), and behind that again is an oil tank of similar construction. Over the whole of the engine, these tanks, and the landing gear, a very neat fairing is built up of sheet Elektron, the engine cowling itself being of the same material and merging into the fairing over the wheel very cleanly. This latter is made in two pieces, the lower forming a fairing round the wheel itself and also a mudguard, sliding up inside the skirt of the upper portion when the Dowty legs are compressed. Dunlop A.H.746 wheels are used, carrying medium pressure 8.5 in. by 10 in. Dunlop tyres and Bendix wheel brakes. The engines are the latest pattern 200 h.p. inverted six-cylinder "Gipsy Sixes." They are fitted with Eclipse direct drive electric starters, and the B.T.H. magnetos are of the small compact kind placed on the top of the engine where they do not cause any bulges in the cowling. A revolution counter with normal flexible drive is carried on the inside of each engine mounting with its dial placed so that the pilot can see it easily from the cockpit. The fuselage is not quite the same as the D.H.86, as the plywood is now placed outside the longerons. The general construction continues to be of spruce and plywood with vertical and diagonal spruce struts wherever necessary. Particular care has been taken to give the fuselage a good shape externally, and with this end in view sheet Elektron curved corner pieces are put over the corners outside the longerons and spruce stringers are run along the fuselage outside the plywood to carry the Titanine-doped fabric with which the fuselage is eventually covered.

The "Office"

The pilot's cockpit, which is not fitted with dual control as standard, is particularly light and airy, with an abundance of windows, giving the pilot a clear outlook in all directions. The windows in the front and at the sides are of Triplex glass, and the latter are both made to open, so that a clear view may be obtained in bad weather. Slightly behind the pilot on either side, and also right over his head, the windows are of cellon carried on a steel tube structure. The controls are normal, with a “spectacle" wheel for aileron control. The wheel operating the tail plane adjusting gear, which is of the screw type, is on the left-hand side of the pilot, below the throttle operating levers. The throttles are actuated by cables passing over large pulleys, but the altitude controls are of the Simmonds-Corsey type. The hand lever for working the Bendix brakes is on the left-hand side of the pilot's seat, and the brakes are also, of course, differentially controlled by the rudder bar in the usual de Havilland fashion. A neat hinged dashboard fills the space below the front window, and carries, besides the usual range of Smith's instruments, an electric fuel gauge made by the same firm, and a Reid & Sigrist Turn and Bank Indicator and a Fore and Aft Level. The switch box controlling the navigation lights and cabin lighting is on the bulkhead behind the pilot. A rudder bias gear is fitted, actuated by a small crank handle near the floor between the pilot's legs, and the foot-rests on the rudder bar itself are fully adjustable over a wide range. The fuel cocks are operated from the cockpit by Simmonds-Corsey controls. The passenger cabin can, of course, be arranged in any manner to suit individual users. The standard arrangement includes accommodation for six passengers with luggage. This first machine is tastefully upholstered in grey by L. A. Rumbold & Co., Ltd., and the tubular chairs are made by the same firm. Cellon windows extend the whole length of the cabin and are set in light alloy frames, while the space between the external plywood structure and the internal upholstery, which is necessitated by the thickness of the longerons and bracing struts, is filled, at the sides of the cabin, with Cabot quilting for sound-proofing purposes. An adequate supply of fresh air is brought into the cabin through a plated duct, placed high up on either side and fed from an inlet in the fairing of each upper wing root.

Controls

The tail units are of the distinctive de Havilland shape and spruce construction. The fin and rudder are plywood covered, and the latter carries a small metal aerodynamic balance in the same manner as that of the D.H.86, which was fully dealt with on page 172 of FLIGHT for February 22, 1934. The tail plane has a plywood leading edge, and the whole is fabric covered, while the elevators are also fabric covered. Great care has been taken with fairing in the tail units to the fuselage, and the tail plane is braced to the fin and fuselage with dual streamline wires. The control surfaces are all worked by Tru-lay cables passing over large diameter pulleys, thus obviating any unnecessary friction. The tail wheel is of the fully castering type, carrying a 10 in. X 3 in. Dunlop tyre, and the taxying shocks are absorbed by rubber blocks in compression. Recently we flew in the new D.H. "Dragon Six" a few minutes after having made a trip in the older type "Dragon," and had an opportunity of making an interesting comparison of the two types. The "Dragon Six" was flying "light" and carried, besides Capt. Hubert Broad, the pilot, only three passengers. The sound proofing arrangements had not then been completed and consequently the machine was somewhat noisy. When, however, it is finished, it is improbable that it will be noisier than the standard "Dragon." The wing area, seen through the windows, appears small compared with that of the earlier type, owing to the sharply tapered wings. Acceleration on the ground was considerably in advance of that of the old model, as was to be expected in view of the improved aerodynamic design and increased power. Although the engines were throttled well back on the climb, we were at 10,000 ft. in a surprisingly short time, and at this height Capt. Broad demonstrated the excellent manoeuvrability of the machine. While we were cruising at below normal power a Leopard “Moth" ("Gipsy Major"), which was looking for us above the clouds, had difficulty in catching up with us, as the cruising speed of the new machine was about 140 m.p.h. As no form of air brake is provided the gliding angle is flat and the actual landing speed is probably 4 or 5 m.p.h. higher than that of the old type. We thought the undercarriage seemed less harsh than that fitted to the standard "Dragon," although there is little cause for complaint regarding the old type of landing gear.

Flight, November 1935

WITHIN the past few months the R.A.F. has given official recognition to a new class of aeroplane, a type intended for coastal reconnaissance and, to a certain extent, for offensive measures against enemy shipping. The tactical uses to which such a machine could be put are legion. In addition to undertaking the duties already mentioned it could be employed to escort torpedo bombers and shipping, to patrol long stretches of coast line, and to undertake antisubmarine work, for which it is provided with bombs. It is now permissible to describe a three-seater coastal reconnaissance version of the Rapide or D.H.89 civil biplane which has been produced by the De Havilland company to perform all these duties. Obviously the machine could also undertake, over land or sea, the multifarious jobs of the general-purpose aircraft, or act as a troop carrier or an ambulance, making it an attractive proposition to air forces in which the economical operation of aircraft is of paramount importance. Structurally the machine is similar to its civilian forerunner, and consequently this description will deal only with the features peculiar to the military version. Actually, it applies to the prototype machine supplied to the R.A.F. The pilot's roomy cockpit is located in the nose of the fuselage. There is an extremely complete instrument board and a tapping key to operate signalling lights both on top of and below the fuselage. On the starboard side is a Mark III Vickers belt-fed machine gun with its breech easily accessible. The feed block is on the left of the gun and cartridges are fed from a box containing 400 rounds beneath the pilot's seat. There is a Very light pistol in the cockpit, which is also provided with a light and dimmer switch, and a drift sight is let into the floor A bomb release is also provided for the pilot. In the front portion of the fuselage, where he can easily talk to the pilot, is the observer-bomber. Just to the real of the pilot's seat is a hole, with a sliding hatch, for bomb sighting purposes, and behind the Vickers gun is an electrical bomb switch with selectors and releases and the handle for opening the sliding hatch which covers the four 20 lb. bombs. As the bomber lies down to sight the bombs he finds an instrument board in front of him, together with an altimeter, A.S.I, and temperature gauge. The navigator's sighting compass, which may be placed on the outside of the machine for taking bearings, is normally situated just above this board. On the left-hand side of the fuselage is the navigator's table with a watch, course and distance calculator and chart board. The bomb load consists of two 100 lb. and four 20 lb. bombs, the former being slung in the middle of the fuselage and accessible from the inside of the machine through the doors of a raised box on the floor. When released they fall through spring-loaded trap doors in the belly of the fuselage which then close automatically after the projectiles have left. Opposite the navigator sits the radio operator, who has a similar table and transmitter, receiver and switchboard mounted in front of him. On the right-hand side of the fuselage is stowage for three parachutes for the crew. Other items are a rack to take four flares and two fire extinguishers and a first-aid box, the latter being accessible from the outside of the fuselage by ripping off a small fabric panel. At the extreme rear of the cabin are the four 20 lb. bombs already mentioned. An ingenious gun mounting of De Havilland design is provided for the rear gunner, who sits on a swivelling seat. The ring itself is mounted on roller races, and it is claimed that, when the gun is fitted, it can be rotated by the pressure of one finger. For any firing position, except that for ground strafing, the gunner sits, and the greater the angle of elevation the higher the position of the gun. In other words, the height of the gun varies with the eye of the gunner instead of the gunner having to adjust his height to that of the gun. When not in use the whole gun and its mounting can be folded away in two or three seconds, the whole being covered by a sliding hatch. Stowage for eight 97-round drums of ammunition is provided. Between the cross tubes of the top centre section is installed a Youngman flotation dinghy which is normally deflated and retained by a three-ply cover. Should the machine descend into the sea, this dinghy is automatically inflated from a cylinder of compressed carbon dioxide, whereupon it bursts its covering and floats, providing means of keeping the machine afloat and of allowing the crew to leave the scene of the descent. Attached to the dinghy are two marine distress signals and a hand inflator.